Issue |
A&A
Volume 419, Number 3, June I 2004
|
|
---|---|---|
Page(s) | 837 - 848 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20034421 | |
Published online | 07 May 2004 |
The 2–8 keV cosmic X-ray background spectrum as observed with XMM-Newton *,**
1
Istituto di Astrofisica Spaziale e Fisica Cosmica, Sezione di Milano “G. Occhialini” – CNR v.Bassini 15, 20133 Milano, Italy
2
Università di Milano Bicocca, Dipartimento di Fisica, P.za della Scienza 3, 20126 Milano, Italy
Corresponding author: A. De Luca, deluca@mi.iasf.cnr.it
Received:
30
September
2003
Accepted:
17
November
2003
We have measured the spectrum of the Cosmic X-ray Background (CXB)
in the 2–8 keV range with the high throughput EPIC/MOS instrument onboard
XMM-Newton. A large sample of high galactic latitude observations was used,
covering a total solid angle of 5.5 square degrees. Our study is based on a
very
careful characterization and subtraction of the instrumental background, which
is crucial for a robust measurement of the faintest diffuse source of the
X-ray
sky. The CXB spectrum is consistent with a power law having a photon index
± 0.06 and a normalization of 2.46 ± 0.09 photons cm-2 s-1 sr-1 keV-1 at 3 keV (~11.6 photons cm-2 s-1 sr-1 keV-1 at 1 keV), corresponding to a 2–10 keV flux of
(2.24 ± 0.16)
10-11 erg cm-2 s-1 deg-1
(90% confidence level, including the absolute flux calibration uncertainty).
Our results
are in excellent agreement with two of the most recent CXB measurements,
performed with BeppoSAX LECS/MECS data (Vecchi et al. [CITE]) and with an
independent analysis of XMM-Newton EPIC/MOS data (Lumb et al. [CITE]),
providing a very strong constraint to the absolute sky surface brightness in
this energy range, so far affected by an ~40% uncertainty. Our measurement
implies that the fraction of CXB resolved by the recent deep X-ray
observations in the 2–10 keV band is of 80 ± 7% (1σ), suggesting the existence
of a new population of faint sources, largely undetected within the current
sensitivity limits of the deepest X-ray surveys.
Key words: X-rays: diffuse background / cosmology: diffuse radiation / surveys / instrumentations: detectors
© ESO, 2004
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